Need advice on motor for mill

[gary350]

Build your own 3 phase converter. You can build one for 1/4 the price of a new one. Its just a capacitor connected to wire L3 long enough to get the motor up to speed then the capacitor is no longer needed. The factory made converters use a relay to do this automatically but you can do the same thing with a normally open push button switch. Push and hold the button then turn on the 3 phase motor. When the motor comes up to full speed release the push button. It is not rocket science anyone can do it and it will cost you $30. You need about 90 MFD per HP to get the 3 phase motor started.

There is another way to do this. Connect a 1/4 hp single phase motor to the 3 phase motor with a V belt and 2 pullies. Turn on the 1/4 hp single phase motor it will bring the 3 ph motor up to speed. Now you turn on the 3 hp motor and turn off the single phase motor. Now the 3 ph motor is running and the 1/4 hp is no longer needed.

There is one more way. Get 2 unused motors. One motor is 1/4 hp single phase the other motor is 3 ph and has to be the same HP rating as the motor on the mill. Use a shaft coupling to connect the to motors together. Start the 1/4 hp motor to get the 3 ph motor up to speed. Next you turn on the 3 ph motor and turn off the 1/4 hp motor. Now that the 3 ph motor is running it can be used as a rotory converter it acts like a 3 phase generator to make real 3 phase but only after it is connected in parallel with another 3 phase motor.

[IdahoJim]

VFD and use the variable speed. You don't need an inverter duty motor in order to vary the frequency.

I'm thinking VFD is the way to go. The original motor is a Baldor, so is probably well-made. It's also reversible, which is a plus, if not a necessity on a mill.
Jim

[IdahoJim]

Build your own 3 phase converter. You can build one for 1/4 the price of a new one. Its just a capacitor connected to wire L3 long enough to get the motor up to speed then the capacitor is no longer needed. The factory made converters use a relay to do this automatically but you can do the same thing with a normally open push button switch. Push and hold the button then turn on the 3 phase motor. When the motor comes up to full speed release the push button. It is not rocket science anyone can do it and it will cost you $30. You need about 90 MFD per HP to get the 3 phase motor started.

Well, heck, if that's all that's involved it should be easy. If it's that simple why aren't more people doing that? So you connect the capacitor to L3...what's the other end connect to, ground?
Jim

[IdahoJim]

Thanks for the input you guys. After reading Gary350's post, and realizing how simple a static converter is, that's what I'm going to build. If I get time this winter, I'm going to build a 3HP rotary converter. That allows me to buy 3 phase tools on a regular basis, providing I only run them one at a time. Before this, I didn't realize these phase converters were as simple as they are. In any case, thanks for all the help.
Jim

[DFMiller]

Jim,
Yes Barker is very much in business. They will make you a brand new one. I think they said they do them in batches. They have a parts manual for sale. It's so much better than the free one on the web. Converting a single axis is not that outrageous. But times 3 adds up. Very sweet machine you have. A rotary phase convertor is not that difficult but VFD's are so cheap. I got a couple on Ebay a while ago for a mill I got but the mill arrived with a roto phase included. 3 phase motor seem to be the way to go.
Good luck.
Dave

[IdahoJim]

Jim,
Yes Barker is very much in business. They will make you a brand new one. I think they said they do them in batches. They have a parts manual for sale. It's so much better than the free one on the web. Converting a single axis is not that outrageous. But times 3 adds up. Very sweet machine you have. A rotary phase convertor is not that difficult but VFD's are so cheap. I got a couple on Ebay a while ago for a mill I got but the mill arrived with a roto phase included. 3 phase motor seem to be the way to go.
Good luck.
Dave

Thanks, Dave. I guess I better get that manual ordered. I hate having a machine without the manual. I'll ask them what it will take to convert the X-axis to screw and handwheel.
I'd like to have a rotophase anyway. It would be nice to have the use of 3-phase tools at full capacity.
Jim

[DFMiller]

Short answer is about $300.00 per axis. :-)
I like my roto phase. If I recall there is a slight derating required when sizing roto phase. I can't remember if there is the same issue with a VFD.
Other observation about roto phase is your motor is running when you have the 3 phase up so when you have your machine off your roto phase unit is still making noise. On the good side they are fairly simple and should last for a long time.
Enjoy
Dave

[IdahoJim]

Short answer is about $300.00 per axis. :-)
I like my roto phase. If I recall there is a slight derating required when sizing roto phase. I can't remember if there is the same issue with a VFD.
Other observation about roto phase is your motor is running when you have the 3 phase up so when you have your machine off your roto phase unit is still making noise. On the good side they are fairly simple and should last for a long time.
Enjoy
Dave

LOL....$300/axis......that's what I paid for the whole mill! Maybe I'll keep my eye peeled for another used one with the handwheel on the x.
Jim

[MTNGUN]

Push and hold the button then turn on the 3 phase motor. When the motor comes up to full speed release the push button.

Turn on the 1/4 hp single phase motor it will bring the 3 ph motor up to speed. Now you turn on the 3 hp motor and turn off the single phase motor.

There is one more way. Use a shaft coupling to connect the to motors together. Start the 1/4 hp motor to get the 3 ph motor up to speed. Next you turn on the 3 ph motor and turn off the 1/4 hp motor.

When I am milling small parts, i am constantly turning the mill on and off, to the tune of several times a minute.

Place a part in the mill, turn on the mill, do the operation. Turn off mill, remove part, place another part in the mill, repeat.

The temptation is to leave the mill running while the finished part is removed and an unfinished part is clamped in the vice ...... but that's not safe.

Personally, I can't get excited about doubling the amount of button pushing. The extra hassle is going to increase the temptation to leave the mill running while parts are clamped and unclamped.

The simple homemade phase converters have their place, but not on a machine that does a lot of start/stop operations.

[Bill Pace]

LOL....$300/axis.....

Thats pretty crazy, huh? - seems typical for parts from the mfgrs...

On that little Barker I had, I converted all 3 axes to 20tpi acme thread with ball crank handles. To get around the problem of making the nuts, I took a page from Evan and made them out of plastic (I think acrylic? - some stuff I had laying around) Cobbled a tap out of a piece of the 20tpi acme - worked plenty good for the 3 nuts needed. Was pretty simple to do and made an interesting project that turned out really nicely -- and the little mill much more usable for the variety of work that comes up in a home ship setting.

I had a bunch of pics of the process, but I cant find them now---

edit....
I did find the post where I showed the making of the ball crank handles----

http://bbs.homeshopmachinist.net/sho...ight=bill+pace